In the fields of the food industry, medicine, electronics industry and the like, for concentration and recovery of useful components, removal of useless components, fresh water generation or the like, a hollow porous fiber membrane that is made of cellulose acetate, polyacrylonitrile, polysulfone, fluorine-based resin or the like using wet or dry-wet spinning, for example, has been widely used in a precision filtration membrane, an ultra filtration membrane, a reverse osmosis filtration membrane, or the like.
In a case where the hollow fiber membrane is manufactured by wet or dry-wet spinning, a membrane forming dope including a hydrophobic polymer and a hydrophilic polymer is firstly prepared. Then, the hollow fiber membrane is formed by a coagulation process of discharging the membrane forming dope in an annular shape and coagulating the membrane forming dope in a coagulating liquid. Here, the membrane forming dope may be introduced into the coagulating liquid through an idle running unit that is in contact with air (dry-wet spinning method), or may be directly introduced into the coagulating liquid (wet spinning method).
Since the hydrophilic polymer normally remains in porous portions of such a hollow fiber membrane in a solution state, the hydrophilic polymer is normally removed by washing or the like, and then, the hollow fiber membrane is dried.
In this regard, in drying the hollow fiber membrane, a hot air circulation drying device, as disclosed in paragraph 0049 of PTL 1, for example, is widely used. Specifically, a method of causing the hollow fiber membrane to continuously run in a drying device in which hot air is circulated at a wind speed of about several meters per second and supplying the hot air to the outer circumferential side of the hollow fiber membrane to dry the hollow fiber membrane is used.